A vehicle, in addition to the inherent crush characteristics of its structure, may have dedicated crash energy management structures. Their function is to dissipate energy in the event of a crash. Such dedicated structures have predetermined crush characteristics which contribute to the resulting deceleration pulse to which the occupants are subjected.
In the vehicular arts there are two known types of such dedicated crash energy management structures: those which are passive, and those which are active.
An example of a passive dedicated crash energy management structure is an expanded honeycomb celled material, which has been used to a limited degree in certain vehicles. FIG. 1 exemplifies the process of fabrication of a honeycomb-celled material. A roll 10 of sheet material having a preselected width W is cut to provide a number of substrate sheets 12, each sheet having a number of closely spaced adhesive strips 14. The sheets 12 are stacked and the adhesive cured to thereby form a block, referred to as a HOBE® (registered trademark of Hexcel Corporation) block 16 having a thickness T. The HOBE block is then cut into appropriate lengths L to thereby provide HOBE bricks 18. The HOBE brick is then expanded by the upper and lower faces 20, 22 thereof being separated away from each other, where during expansion, the adhesive strips serve as nodes where the touching sheets are attached to each other. A fully expanded HOBE brick is composed of a honeycomb celled material 24 having clearly apparent hexagonal cells 26. The ratio of the original thickness T to the expanded thickness T′ is between 1 to 20 to 1 to 60. An expanded honeycomb celled material provides crash energy management parallel to the cellular axis at the expense of vehicular space that is permanently occupied by this dedicated energy management structure.
Typically, crash energy management structures have a static configuration in which their starting volume is the same as their fixed, operative volume. When involved in a crash, they dissipate energy and modify the timing characteristics of the deceleration pulse by being compressed (i.e., crushing or stroking of a piston in a cylinder) from a larger to a smaller volume. Since these passive crash energy management structures occupy a maximum volume in the uncrushed/unstroked, initial state, they inherently occupy vehicular space that must be dedicated for crash energy management. Expressed another way, passive crash energy management structures use valuable vehicular space equal to their initial volume which is dedicated exclusively to crash energy management throughout the life of the vehicle even though a crash may never occur, or may occur but once during that time span. This occupied space is not available for other uses, including functions such as enabling a more spacious vehicle interior and styling flexibility.
For example, the fixed fore-aft location of a knee bolster may constrain how far the lower portion of the instrument panel can be placed forward and away from the knees of an occupant.
Active crash energy management structures have a predetermined size which expands at the time of a crash so as to increase their contribution to crash energy management.
One type of dedicated active crash energy management structure is a stroking device, basically in the form of a piston and cylinder arrangement. Stroking devices have low forces in extension and significantly higher forces in compression (such as an extendable/retractable bumper system) which is, for example, installed at either the fore or aft end of the vehicle and oriented in the anticipated direction of crash induced crush. The rods of such devices would be extended to span the previously empty spaces upon the detection of an imminent crash or an occurring crash (if located ahead of the crush front). This extension could be triggered alternatively by signals from a pre-crash warning system or from crash sensors or be a mechanical response to the crash itself. An example would be a forward extension of the rod due to its inertia under a high G crash pulse. Downsides of such an approach include high mass and limited expansion ratio (1 to 2 rather than the 1 to 20 to 1 to 60 possible with a compressed honeycomb celled material).
Another type of active dedicated crash energy management structure includes inflatable air bags or pyrotechnic air cans. Downsides of such systems, in addition to those discussed above, include low force levels and low ratios of crush force to added mass due to the lack of mechanical rigidity of these systems.
As such, what has further been sought in the vehicular arts is a dedicated vehicular crash energy management structure which provides, at times other than a crash event, open spaces for other uses than crash pulse management, a high crush force, and a high crush force to mass ratio. Examples of some such active and passive devices are detailed, for example, in U.S. Pat. No. 6,702,366 the contents of which are incorporated by reference herein. U.S. Pat. No. 6,702,366 provides for both active and passive crash energy management structures. Specifically, U.S. Pat. No. 6,702,366 describes the use of a honeycomb celled material, such as that described above that expands from a dormant state to a deployed state at around the time of a crash. U.S. Pat. No. 6,702,366 does not provide for specific deployment means of the honeycomb celled material.
However, existing occupant restraint devices and crash energy management devices have not been provided with deployment means since most of such devices are of a fixed size and placement and merely deform to absorb crash energy or restrain vehicle occupants or pedestrians. Thus, there has been little development of deployment means for such devices. Accordingly, what remains needed in the vehicular arts is a means for deploying a volume-filling mechanical structure from a smaller dormant state to a larger deployed state at around the time of a crash event.